Analysis and comparison of various energy storage method

Energy storage is the conversion of electrical energy into other forms of energy for storage. The basic energy storage method is to first convert electricity into other forms of energy and store it in an energy storage device, and release it when needed.

According to the characteristics of energy conversion, electrical energy can be converted into kinetic energy, potential energy and chemical energy. In China, power conversion system companies are specialized in energy conversion and they have rich experience. To get further understanding, you can read the top 10 power conversion system companies article.

The purpose of energy storage is mainly to realize the stable operation of power at the supply end, transmission end, and user end. The specific application scenarios include:

1. It is applied to the fields of power grid peak shaving and valley filling, smoothing load, and quickly adjusting grid frequency to improve the efficiency of power grid operation and make sure its stability and reliability;
2. Applied in the field of new energy power generation to reduce the impact of large instantaneous changes in photovoltaic and wind power generation systems on the power grid;
3.  Applied to new energy vehicle charging stations, Reduce the impact of large-scale instantaneous charging of new energy vehicles on the power grid, and enjoy the power price difference between peaks and valleys.

The energy storage system realizes the charging and discharging of electric energy

The main types of energy storage currently on the market include physical energy storage and electrochemical energy storage method. According to different energy conversion method, energy storage can be divided into physical energy storage method, electrochemical energy storage method and other energy storage method:

• Physical energy storage

Physical energy storage is a kind of energy storage method and it includes pumped water storage, compressed air energy storage and flywheel energy storage, among which pumped storage Large capacity and low kWh cost are currently the most widely used energy storage method in physical energy storage.

• Electrochemical energy storage

Electrochemical energy storage is a type of energy storage method that has developed rapidly in recent years, mainly including lithium-ion battery energy storage, lead-acid battery energy storage and flow battery energy storage; among them, lithium-ion batteries have the characteristics of good cycle characteristics and fast response speed. 

• Other energy storage methods

Other energy storage method include superconducting energy storage and supercapacitor energy storage, which are currently less used due to high manufacturing costs and other reasons.

Physical energy storage and electrochemical energy storage

Energy storage is mainly used in power grid transmission and distribution and auxiliary services, renewable energy grid connection, distributed and micro-grid, and various parts of the user side. In terms of grid transmission and distribution and auxiliary services, the main functions of new energy storage technology are grid peak regulation, loading, starting and alleviating transmission congestion, and delaying the upgrade of transmission and distribution networks.

In terms of grid connection of renewable energy, energy storage method is mainly used to smooth the output of renewable energy, absorb excess power to reduce "abandoning wind and light", and instant grid connection. In terms of distributed and microgrids, energy storage is mainly used to stabilize system output, serve as a backup power supply, and improve scheduling flexibility; on the user side, energy storage is mainly used for industrial and commercial peak-shaving and valley-filling, demand-side response, and energy cost management.

Energy storage has a wide range of application scenarios

The world energy storage market continues to develop steadily, and the cumulative installed capacity has reached 179.1GW. The energy storage industry emerged early and developed steadily. By the end of 2010, the cumulative installed capacity of energy storage had reached 135GW.

During the period from 2010 to 2015, due to the impact of the overall economic downturn, the growth rate of the overall installed capacity slowed down. By 2015, the cumulative installed capacity reached 144.8GW; from 2016 to 2018, due to the dual stimulation of cost reduction and policy promotion, the energy storage industry developed rapidly, and the cumulative installed capacity reached 179.1GW by the end of 2018.

The installed capacity of energy storage continues to rise

Pumped storage occupies an absolute dominant position, and electrochemical energy storage is growing rapidly. According to the data, as of the end of 2018, pumped storage accounted for 94.3% of the world's installed capacity, occupying an absolute dominant position. This kind of energy storage method reached 3.7%, and other energy storage method such as molten salt heat storage and compressed air accounted for a relatively low proportion of the multi-component energy storage market, accounting for only 1.5% and 0.2% respectively.

Similar to the world market, the Chinese market is dominated by pumped storage. According to CNESA statistics, as of the end of 2018, pumped storage accounted for 95.8% of China's overall installed capacity of energy storage, and electrochemical energy storage method coexisted with other energy storage method, of which accounted for 3.4%. The thermal energy storage market accounted for 0.7%, while the flywheel energy storage and compressed air energy storage markets accounted for less than 0.1%.

According to the data, China's energy storage installed capacity is mainly distributed in Northwest China and East China, which together account for 49% of the total installed capacity. Among them, the northwest region is mainly concentrated in Xinjiang and Gansu provinces, and the east China region is mainly concentrated in Jiangsu, Zhejiang and other provinces. In addition, the proportion of installed capacity of energy storage in Southwest China, South China and North China is estimated to be 14%, 12% and 15% respectively.

Southwest China is mainly concentrated in Yunnan Province, South China is concentrated in Guangdong Province, and North China is mainly concentrated in Shandong, Shanxi and China. Inner Mongolia and other provinces. The installed capacity of energy storage in Central China and Northeast China is very small, accounting for 5% of the total. The installed capacity of energy storage is mainly concentrated in Hunan and Liaoning provinces.

The electrochemical energy storage lithium-ion batteries continues to rise

Lithium-ion batteries account for nearly 90% of the world's installed capacity of energy storage method. China came from behind, accounting for 17.3% of the world's installed capacity of energy storage method. Electrochemical energy storage started late, and lithium-ion batteries boosted China to catch up. Although China's electrochemical energy storage started late, its installed capacity has always remained at a relatively high level. In 2011, the installed capacity of it in China was only 40.7MW.

By 2017, the cumulative installed capacity had reached 389.3MW, 9.6 times that of 2011. 2018 was a year when the industry as a whole exploded. Benefiting from the rapid advancement of grid-side projects and the gradual decline in battery costs, China added 682.9MW into operation in 2018, a year-on-year increase of 464.4%, and the cumulative operation scale reached 1.073GWH. Breaking through the GW level for the first time, it is 2.8 times the total scale of cumulative operation in 2017.

From the perspective of battery type, lithium-ion batteries account for 70%, and lead-acid batteries are still popular in the market due to their low cost, accounting for 27%. China's electrochemical energy storage market is dominated by lithium-ion battery energy storage, and lead-acid battery energy storage is an important component.

In the distribution of new installed capacity of electrochemical energy storage in China in 2018, lithium-ion batteries accounted for 70.6% of the installed capacity; lead batteries are an important supplement to the electrochemical energy storage market, accounting for 27.2% of the newly installed capacity. The remaining energy storage method such as flow batteries, supercapacitors, and sodium-sulfur batteries accounted for only 2.2% in total.

Development of chemical energy storage in China

In China, lithium batteries energy storage method accounted for 70%, and lead-acid batteries accounted for nearly 30%. Lithium-ion batteries are used in a wide range of applications. Compared with traditional batteries, lithium-ion batteries do not contain heavy metals such as lead and cadmium, are pollution-free, and do not contain toxic materials. They also have the characteristics of high energy density, high working voltage, light weight, and small size.

They have been widely used in consumer electronics, New energy vehicle power battery and energy storage field. Lithium-ion battery cells are mainly composed of four major materials: positive electrode material, negative electrode material, electrolyte and separator.

From the battery cell to the final complete battery pack, there are mainly two steps:

1. Connect a certain number of cells in series and parallel assembled into a battery module;
2. The battery module plus a thermal management system, a battery management system (BMS) and some structural components form a complete battery pack, also known as a battery pack.

The lithium-ion battery industry chain involves upstream non-ferrous metal materials, midstream battery materials and batteries, and downstream power batteries, consumer batteries and energy storage battery applications. There are many lithium battery technology routes, and energy storage pays more attention to safety and long-term cost. Compared with power lithium batteries, lithium batteries for energy storage have looser requirements on energy density, but higher requirements on safety, cycle life and cost.

From this point of view, lithium iron phosphate battery is a more suitable technical route for energy storage among various lithium-ion batteries at this stage, and most of the lithium battery energy storage projects that have been put into construction at present also adopt this technology. The main advantage of the ternary battery is its high energy density, but its cycle life and safety are relatively limited, so it is more suitable for use as a power battery.

Lithium iron phosphate is more suitable for energy storage applications due to its high cycle times and good stability. The application of lithium-ion battery energy storage technology is mainly concentrated on the grid connection and grid side of renewable energy. From a global perspective, the grid side is the most widely used lithium battery energy storage technology, accounting for 52.7%, mainly used for peak and frequency regulation of the grid.

Renewable energy grid-connected accounted for 28.9%, distributed and micro-grid and user-side accounted for 13.2% and 5.2% respectively. The Chinese market is slightly different, and the grid-connected application of renewable energy accounts for the highest proportion, reaching 37.7%. Followed by grid-side applications, user-side and micro-grid, accounting for 25%, 22.1% and 13.2% respectively.

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